Manufacture of cellulose ethers



Patented Mar. 16,1043

2,313,866 mum-scrum: or cnracmsn ETHERS Alexander 8. Finlayson, Hopewell, Va., assignor to Hercules Powder Company, Wilmington, Del., a

corporation of Delaware Application September 8, Serial No. 355.600

No Drawing.

.4 Claims. (01. 260-231) This invention reiatesto an improved method for the alkylation of cellulose, and more particularly to an improved method for the alkylation of sheet cellulosic material to produce cellulose 353s of high quality and commercial accepta- Heretofore the art has manufactured cellulose ethers from cellulosic materialby'two general processes: The first process includes two steps,

(1) the production of alkali cellulose by steeping cellulosic sheets in concentrated caustic alkali followed by the removal of the caustic liquid.

- This alkali cellulose is usually in the forxnof sheets known as pulp board and before being etherifiedmust be disintegrated by a shredding machine and (2) the treatment of this alkali cellulose with an alkyl chloride such as, for example. ethyl chloride; and additional quantity of alkali, and, usually, a diluent such as benzene or toluene. This admixture is heated with vigorous introduced by the mastication step and I produced cellulose ethers of very highquality.

The advantages which I obtain by using this chipped, cellulosic material rather than other formsof raw cellulose, in'the preparation of the alkali cellulose, is due to theuniformity of the size of the particles and their tendency to partially retain the original sheet structure, conducive' to the quick wetting and-free swelling of stirring untiletheriiication has proceeded to the v proper degree. The first step comprising the production of alkali cellulose is a very expensive procedure as it requires considerable time, expensive ingredients and expensive equipment and it has been found by the art that although alkali cellulose will give high quality ethyl cellulose it is impractical to use it incommercial production due tothetimeandmoneyrequired. I

The second general method which has been developed to obviate the need of manufacturing .aikali cellulose as an intermediate comprises a one step process in which the cellulose, alkali,water, etherifying agent and diluent are all added directly'to a reaction vessel and heated with vigorous agitation until the proper degree of etheriiication is reached; This method simplifies the prooedure byavoidingj the separate productionpf alkali but gives a product that is nonimiform, and not of commercial quality. This method has not found commercial application in spite of its inherent simplicity.

Now Ihave found that I can entirely eliminate the mastication step or materially reduce the ex-- tended time which it has heretofore consumed and'still obtain the uniform alkylation required for a satisfactory commercial product. I accom- 1 plish this by shipping a fibrous cellulosic material in form of a loosely felted sheet by the method described in U. S. Patent 2,028,080 to Raphael L.

Stern, prior to the incorporation or wetting. there'- of with arr-aqueous alkalisolution. By. so-doing, I not only eifect-a material saving in time and in power required for the mastication, but I also largely avoid the metal contamination heretofore 5c alpha-cellulose content of- 8896, 959! or such the fibers during the formation of alkali cellulose. After shredding the sheet cellulosic material to a suitable size prior to the addition of aqueous alkali solution no masticating operation is required. All that is required to form an alkali cellulose is the uniform mixing of the chipped cellulosic material with the desired amount of the aqueous alkali solution either by a short stirring,

operation or by spraying the aqueous alkali upon the chipped cellulose.

By the method in accordance with this invention, a relatively thin sheet of loosely felted, fl-' brous cellulosic material. is cut or chipped into I lengths, preferably of a'width less than the thick-.

ness of the sheet, and at the same time the lengths will be separated lengthwise into two 'or more lengths which, respectively, will be of a thickness less than the thickness of the sheet. Hereinafter, -I shall refer to a cellulosic material which is cut or chipped in this way as chipped cellulose." The resultant chipped cellulose is then uniformly admixed and incorporated with an aqueous alkali solution either by stirring or spraying and themmixture treated with an alblating agent such as, for example, an alkyl halide, a dialkyl sulfate, etc.,

for a period of time suiiicient to give a uniform alkylation of. the cellulose. ,The resultantalkyl cellulose is then'recovered from the reaction mixture by one of the methods known to the art.

The chipped cellulose formed by the cutting or chipping operation will'be comprised of lengths of looselyfelted fibers. The ends and surfaces oi the lengths will be irregular and will have protruding fibers. The cellulose may conveniently be put into this form by cutting orchipping in the mechanism described in detail in s. Patent 2,028,080. The cellulose which I utilize inthe method in accordance with this invention will desirably be in the form of loosely felted, fibrous sheets and a will be of any type suitable for chemical treatment. It maybe, for example; wood pulp or'ootton linters, of types suitable for chemical treatment, in the form of felted sheets. Thus for examplerthe woodpulp I' utilize may have an The sheet from which the thread-like or ribbe recovered unchanged at the end of the reacbon-like lengths of chipped cellulose'will be formed may be, for example, of any commercial form of felted wood pulp or'felted cotton linters, suitable for use in the manufacture of alkyl ethers of cellulose. The sheet may be of any width, depending upon the capacity of apparatus designed to cut oi the thread-like lengths which I treat with an aqueous alkali solution. The sheet may be ofa thickness within quite wide limits, say, from about 0.02 to about 0.05 inch.

By way of illustration and not by way or limitation a sheet of lightly felted cellulose having a thicknessof 0.030.inch may. be used. The chipped lengths formed from this sheet will desirably have a length, of say, about inch. to about 2 inches and desirably about inch. They will desirably have a width of about 0.015 inch and a thickness of about 0.010 inch; These lengths having a thickness ;of about 0.010 inch, will be formed by the cutting of 0.015 inch widths of a length of inch from the sheet and separating lengthwise into three pieces. The lengths will be thread-like or ribbon-like depending upon their-width. The separating of the lengthsicauses their upper and lower surfaces to be irregular or rough with protruding Lflbers. Their edges will be irregular or rough due to the tearing, as well as the shearing action, .of the cutting edges of the chipping machine.

The amount of alkali used, preferably caustic soda, will be any quantity customarily used by. the .art in the alkylation of cellulose. I have found that 'it is usually desirable to use an "amount of alkali within the range of about "mols to about 34 mols, and preferably within the range of about 16 mols to about 28 mols, to

each mol of cellulose-(calculated as CeHroOs) present, depending uponthe desired alkoxy content of the product. p The concentration of the aqueous alkali solution which I utilize will desirably be adjusted for convenient incorporation or spraying of the above indicated quantities ofthe alkali with the chipped cellulose material,

, preferably the aqueous alkali will be 50% caustic. The alkylatlng agent used may be an alkyl ,halide or'a'ny' alkyl sulfate and preferably, an

alkyl chloride. Thus, for example, an alkylating agent may-bemethyl chloride, dimethyl sulfate,

ethyl chloride, ethyl bromide, diethyl sulfate,

propyl chloride, propyl bromide, butyl bromide, butyl chloride, etc. An alkylating agent will, of

course, be chosen which contains the alkyl group that is desired in the cellulose ether, and it will be found that the method in accordance with this invention is applicable to the production of any of the alkyl cellulose ethers heretofore known and highly advantageous therein. Celluhaving a good solubility in organic solvents, I prefer to use a large excess of alkylating agent.

Thus, I may use 7-15 mols of alkyl chloride to each cellulose unit. The alkylating agent serves not only as a reactant, but also as a medium for the reaction, and a large part of the excess may' tion.

This excessof alkylating agent may be replaced to a greater or lesser extent by an organic solvent, such as, for example, a lower aliphatic alcohol or ether, benzene, toluene, dioxan, etc. Which acts both as a diluent (medium for the reaction), and as a solvent for the cellulose ether formed. The alcohol used may be a lower ali- 'phatic aicohol-sucwasgfor example, methanol,

ethanol, n-propan'ol, isopropanol, n butanol, etc.- To avoid. the formation of e an excessive number of by-products, I prefer to use an alcohol cone taining the same alkyl group as thatcontained in the alkylating agent. The time required to complete the reaction in the presence of such diluent is greater, than when an excess of the alkylating agent serves as a medium for the re-' action.

c I When using an alkyl chloride as an alkylating agent, as I prefer to do, the reaction is carried out in an autoclave, provided with a stirrer or constructed for. rotating or; tumbling motion to ethyl chloride as an alkylating agent, a ternperature within the range of about C. to about 150 C. and preferably, within the range of about C; to about C. will be found satisfactory. It will be found that the higher the temperature, the more rapid the reaction, while the lower temperature results in greater uniformity.

As further illustration. ofthe method in accordance with this invention I may cite the following examples: f

- Exmrns I E Lightly felted sheet wood pulp having a thickness of 0.030 inch was chipped into lengths of about inch, a width of about 0.015 inch and a.

thickness of about 0.010 inch. One part by weight of this chipped or shredded wood Pulp was covered with 14 parts by weight of a caustic soda solution having ea/concentration of 50% by weight and stirred for 15 minutes during which time the chips became thoroughly wetted. The resulting wetted cellulose and free caustic solution were transferred to a high pressure autoclave. About 4.5 parts'by. weight of ethyl chloride were. then added to the autoclave and the reaction allowed to continue for a period of 12 hours at a temperature within the range of about 80 to C. The ethyl cellulose was then precipitated from the reaction mixture by distilling out the residual ethyl chloride and byproduct ethyl ether and ethyl alcohol formed by being masticated for a period of 4 hours after I soaking tor a period or 8 hours in a caustic soda solution. Exam-u II linterswas mixed with 14 parts by weight oi a 50% aqueous solution oi caustic soda for 15 minutes. The resulting mass was transferred to an-autoclave and ethylated by the procedure described in Example I. :The finished product,

havingan ethoxy content of about 47.9% was Ex suru 111 One part by weight of lightly felted cotton linter sheets were chipped in accordance with Example I and the chipped materiaisprayed with about iii parts by weight 50% sodium hydroxide solution. The chips wetted by the aqueous caustic were charged directly into an autoclave and about 4.3 parts by weight of ethyl chloride added thereto. The mass was continuously stirred for about 12 hours during which period the temperature was raised to about 140 C. The volatile organic solvents were then distilled from the autoclave and the ethyl cellulose recovered from the spent caustic. The product produced was of high quality and gave clear solutions.

In accordance with the procedure of Example 7 111 series oi ethylations were carried out'using first sheeted cotton linters and second clipped cotton linters, as the cellulose material. The ethyl cellulose produced in each ethylation was tested ior turbidity with a Betz-Hellige Turbidimeter and showed the results given below in Table I.

.From the above ,resultsit is obvious that the turbidityoi ethyl cellulose solutions is greatly improved by the use of thechlpped cellulose'in acoordance with this invention. 'The Beta-Hel lige Turbidimeter is a standard instrument and One part by weight of shredded sheet cotton round to give solutions 0'! high clarity and to the results are expressed as grams of barium sulphate per 60 cc. of distilled water measured at a depth 01' 20 mm. In the runs above the only variable ifioduced in the manufacture method, Example ,was the form of the cellulose used. The mechanical advantage of eliminating th 2 expensive and time consuming mastication operation and the improved quality of cellulose ether produced especially as to turbidity which are accomplished by the method oi. my invention are definite advantages in the ethyl cellulose art and ails possible only through the use of chipped cell ose.

The diilerence in the chipped cellulose and sheet cellulose is specifically shown by a comparison of the bulk density of the two materials. Bulk density is determined as pounds of material under its'own weight, per cubic foot. Some bulk density values or sheeted cotton linters and wood pulp and chipped cotton linters and wood pulp are given in Table 11 below and conclusively demonstrate the extreme bulkiness oi the chipped cellulosic material.

Table 1:

Bulk density Sample Shredded Bheeted Lei m n. Lbs/emit.

Cotton iinters... 8. 8-4. 2 21-85 Woodpulp 24-3.! 20-50 The process in'accordance with 'my invention allows the production of cellulose ethers from cellulosic material in a simplified manner and provides a high quality product which shows improvement over prior art products in clarity 0! solutions and a decrease in the amount 0! unetherlfied particles. The invention provides a cellulosic material which is obtainable at a reasonableprice, is easy tohandle, requires no masticationprocess, is easily wetted, and produces a product of good color and solubility;

It will beunderstood that the details and ex amples hereinbeiore set forth are illustrative only and that the invention as broadly described and claimed is in no way limited thereby.

nly c'opending application, Serial No. 228,887,

This application is a continuation-in-part of and desire to protect by Letters posed of fibers selected from the group consisting 0! wood and cotton cellulose fibers which consists in chipping the sheet cellulose to threadlilre or ribbon-like lengths and separating the lengths longitudinally to form chipped lengths having rough irregular ends and surfaces with protruding fibers, an open physical structure 'conducive to quick uniiorm wetting by aqueous alkali solution. and'an apparent bulk density between'about 2.4 and about 4.2 pounds per cubic foot; unii'ormly wetting the said chipped lengths with an aqueous solution oi. alkali-metal hydroxide of aconcentration forming alkali cellulose capable of reacting with an alkylating agent to form a cellulose ether soluble in organic solvents by lightly agitating the chipped lengths ior notmore than 15 minutes with the alkali solution; heating the resultins'wetted cellulose I with a lower alkyl etherifying agent under etheriiying-conditions until a cellulose ether soluble in organicsolvents is obtained; and recovering and cotton cellulose fibers which consists in chipping the sheet cellulose to thread-like or ribbonlike lengths and separating the lengths longitudinally to form chipped lengths having rough irregular ends and surfaces with protruding fibers, an open physical structure conducive to quick uniform. wetting by aqueous alkali solution, and an apparent bulk density between about 2.4 and about 4.2 pounds per cubic foot; uniformly wetting the said chipped lengths withan aqueous solution-of alkalimetal hydroxide of a concentration forming alkali cellulose capable of reacting with an ethylatm gent to form ethyl cellulose soluble in organic solvents by lightly agitating the chipped lengths for not uniformly wetting w an aqueous solution of sodium hydroxide'of a concentration forming alkali cellulose capable of reacting withan ethylating agent to form agitating the resulting wetted cellulose with ethyl chloride under 'etherifying conditions at-a temperature between about 90 C. and about 150 C.

- until ethyl cellulose soluble in organic solvents is obtained; and recovering the ethyl cellulose.

4. A process for manufacturing cellulose alkyl ethers low in turbidity and soluble in organic solvents from lightly'feltedsheet cellulose commore than minutes with the alkali solution;

heating and agitating the resulting wetted cellulose with ethyl chloride under etherifying conand cotton cellulose fibers which consists in chipping the sheet cellulose to thread-like or ribbonlike lengths and separating the lengthslongi- I tudinally to form chipped lengths having rough I irregular ends and surfaces with protruding fibers, an open physical structure conducive to quick uniform wetting by aqueous alkali solution, and an apparent bulk density between ing of wood and cotton cellulose fibers which consists in chippin the sheet cellulose to threadlike or ribbon-like lengths and separating the lengths longitudinally to form chipped lengths having rough irregular ends and surfaces with protruding fibers, an open physical structure conducive to quick uniform wetting by aqueous alkali solution, and an apparent bulk density between about 2.4 and about 4.2 pounds per a concentration of about in a quantity conthereby; heating and agitating the resulting" wetted cellulose with ethyl chloride in a quantity' of 7l5 mols for each Col-11.005 mol of celluabout 2.4 and about-4.2 pounds per-cubic foot;

lose under etherifying conditions at a temperature between about C. and about C. until ethyl cellulose soluble in organic solvents is obtained; and recovering the ethyl cellulose.

- ALEXANDER. S. FINLAYS ON.

the said chipped lengths with 

